This invention pertains to the field of electrical illuminating apparatus and particularly to such apparatus which is permissible under Mining Enforcement and Safety Administration (MESA) standards and regulations for use in explosive atmospheres such as coal mines.
Lighting in mines has always been relatively poor compared to working environments above ground where minimum illumination standards for various tasks have long been established.
The difficulty of providing adequate lighting in coal mines is aggravated by the low reflectivity of the black coal or associated minerals in the roof, floor, and side walls. Rock-dusting where employed does provide a reflective white or light gray surface along established haulage ways and heavy traffic areas such as underground maintenance shops, areas immediately adjacent the bottoms of hoisting shafts, and loading points along conveyors. These locations are relatively well-lighted with permanent lighting.
By contrast, rooms where coal is actively being mined are relatively poorly lighted. These rooms have not yet been rock-dusted and the freshly exposed black surfaces provide no practical reflectivity. Illumination is provided only by miners' cap lamps and one or more high intensity headlight-type lamps on each piece of mobile mining machinery. In the case of shuttle cars, which operate in both directions, there will be one or more headlights on each end. Even where such high intensity lamps are directed toward the face, or toward the direction of movement of the machine, lighting is far from uniform. The operator of a continuous mining machine, or loading machine, will have enough light brilliantly illuminating the mine face to keep his machine working efficiently. but the rear boom just behind him is in relative darkness making it difficult for him to see a person immediately behind or to the side. Inasmuch as these face-working machines have conveyor discharge booms which are tiltable up and down, and swingable from side to side, there have been numerous accidents involving persons unseen by the machine operators being struck by the discharge booms and pressed against another machine or one of the side walls.
MESA reports show that almost all serious and fatal accidents in working places occur while self-propelled equipment is operated in them.
Pursuant to authority under the Federal Coal Mine Health and Safety Act of 1969, the Secretary of the Interior has promulgated new illumination standards for underground coal mines which, among other things, specify that the entire area surrounding self-propelled mining equipment for a minimum distance of 5 feet be illuminated with a surface brightness of at least 0.06 footlamberts.
To provide this level of illumination, something more efficient than conventional incandescent lamps must be used. A few attempts have been made to develop fluorescent lighting which is permissible for use in potentially explosive atmospheres such as coal mines, and which could provide the high level of illuminations required by the new standards, but none of these attempts have yet been successful enough to warrant large scale production and use.